1. Field of the Invention
The present invention relates to an apparatus for measuring a specific absorption rate (hereinafter, referred to as an “SAR”), and in particular, to an apparatus for measuring an SAR of a radio communication apparatus such as a mobile phone, a portable radio communication apparatus, or the like.
2. Description of the Related Art
Recently, portable radio communication apparatuses such as a mobile phone have spread greatly. Accompanying this, a problem regarding the influence of electromagnetic waves radiated from a portable radio communication apparatus onto a human body has been caused. As a general index of the influence, an SAR is provided. The SAR is an electric power absorbed by a unit mass by exposing a living body such as a human body or the like to an electromagnetic field, and is expressed by the following Equation (1):SAR=(σE2)/ρ  (1),
where E [V/m] is an electric field intensity, σ[S/m] is an electrical conductivity of an organic tissue, and ρ [kg/m3] is a density of the vital tissue.
In an SAR evaluation method or a so-called electric field detecting probe method as explained in “Method for Measuring Specific Absorption Rate of Mobile Phone or the like Used on Human Temporal Side” in Telecommunications Technology Council Report of the Ministry of Public Management, Home Affairs, Posts and Telecommunications in Japan, a human body model or so-called phantom is used that simulates a shape, a size, and electric characteristics of cephalic tissues electric characteristics. Using this phantom, an SAR which may be generated in the human body is experimentally estimated (See a first prior art document of “Standard of Specific Absorption Rate (SAR) Estimation Method for Portable Radio Terminal”, ARIB STB-T56 Ver. 2.0, Revised on Jan. 24, 2002, Association of Radio Industries and Business in Japan (“ARSB”)).
Legal regulations for the SAR have been enforced globally. For this reason, it is essential to conduct an SAR check in a manufacturing process of a portable radio communication apparatus such as a mobile phone or the like. To this end, a method and an apparatus capable of simply, promptly conducting the SAR check are required. There has been conventionally proposed, as a simple SAR estimation method, an estimation method for experimentally estimating the SAR based on a magnetic field intensity H on a surface of the phantom in, for example, a second prior art document of N. Kuster et al., “Energy Absorption Mechanism by Biological Bodies in the Near Field of Dipole Antenna Above 300 MHz”, IEEE Transaction on Vehicular Technology, Vol. 41, No. 1, pp. 17-23, February 1992. With this conventional method, it has been confirmed that a relationship expressed by the following Equation (2) is established for the distribution of an SAR as generated on a surface of the human body:SAR∝H2  (2).
There is disclosed as a conventional SAR estimation method, an SAR estimation method for calculating an electric current distribution from an incident magnetic field on the surface of the phantom when an electromagnetic wave is radiated from an antenna to obtain the SAR distribution in, for example, the Japanese Patent No. 2790103. With this conventional SAR estimation method, the magnetic field is detected by a magnetic field detecting probe that includes movement and rotation mechanisms, then the electric current distribution of the antenna is thereby estimated, and the SAR is evaluated from this electric current distribution.
In the actual measurement of the SAR, it is necessary to do so under various conditions including the arrangement of the mobile phone relative to the head of the phantom, a type of the antenna, and an arrangement state of the antenna. The maximum SAR of measurement results under the various conditions is set as an SAR of the mobile phone. For this reason, it takes a considerably long time to measure the SAR. Even if the simple SAR measuring method mentioned above is used, the arrangement of the portable radio communication apparatus with respect to the phantom should be changed. Further, in the actual SAR measurement, the SAR is measured with the mobile phone closely attached to the phantom. With the conventional method disclosed by the Japanese Patent No. 2790103, the incident magnetic field on the surface of the phantom is measured. Due to this, the magnetic field cannot be measured while the mobile phone is arranged in accordance with the actual SAR measurement. It is, therefore, disadvantageously impossible to check the SAR of the mobile phone on the production line by the conventional SAR measuring apparatus or method.
Moreover, according to the prior art, the SAR of the portable radio communication apparatus is measured while the apparatus is closely attached to the head of the human body. For this reason, an actual surface magnetic field cannot be measured, and an error is generated in the measured SAR. In addition, when the portable radio communication apparatus, an ordinary dipole antenna, or the like is employed as a reference antenna, a part having a low magnetic field intensity locally may be caused, and magnetic field detection precision is deteriorated. As a result, an SAR estimation error is disadvantageously generated.